Data packets, which originate, for example, from local area networks, are transmitted through data networks to respective addressees. Such data packets originate particularly from Internet applications, are structured in accordance with the Internet protocol (IP), and have a source address and a destination address. As transmission media (OSI Layer 1) for long-haul data communications networks, synchronous digital networks based on the SDH or SONET standards and recommendations are used (SDH=Synchronous Digital Hierarchy, SONET=Synchronous Optical Network). This is stated, for example, in RFC 1619 (W. Simpson, Request for Comments 1619, Internet Engineering Task Force, Network Working Group, May 1994), which proposes to place data packets to be transferred over point-to-point links directly in synchronous transport modules (STM-N) of SDH or synchronous transport signals (STS-N) of SONET.
In synchronous digital communications networks, virtual, i.e., logical, connections can be switched between elements of the network. This is done manually with the aid of a management system. The switched logical connections are then used by routers of different data networks, which provide the gateways to the synchronous digital communications network, to transmit data packets.
Since applications of the Internet, in particular, produce widely time-varying data quantities (between 0 b/s and a few Mb/s) which have to be transmitted over the synchronous digital communications network in the form of IP data packets, the prior art has the disadvantage that either large transmission capacities have to be kept available in the communications network, which then remain unused most of the time, or that bottlenecks occur if several users want to send large amounts of data simultaneously.
In another concept, IP packets are first placed in ATM cells and then transmitted over virtual channel connections through a synchronous digital communications network (SDH or SONET). In an article published by Ipsilon Networks ("IP Switching: The Intelligence of Routing, the Performance of Switching", Ipsilon Technical White Paper on IP Switching, February 1996, retrievable in the Internet at http://www.ipsilon.com/productinfo/wp-ipswitch.html), a device (IP Switch) is presented which combines the functions of an IP router and an ATM switch. This device is capable of identifying longer-duration sequences of data packets having the same source and destination addresses, so-called flows, by means of an address monitor, and to switch suitable connections for these flows in the hardware. This increases the throughput of data packets through the IP switch and shortens the mean switching time. This, too, has the disadvantage that only predetermined logical connections can be used, which are either underdimensioned or overdimensioned, depending on the current payload.